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<title>Berkeley DB Reference Guide: Configuring locking</title>
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<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Locking Subsystem</dl></b></td>
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<p align=center><b>Configuring locking</b></p>
<p>The <a href="../../api_c/env_set_lk_detect.html">DB_ENV-&gt;set_lk_detect</a> method specifies that the deadlock detector
should be run whenever a lock is about to block.  This option provides
for rapid detection of deadlocks at the expense of potentially frequent
invocations of the deadlock detector.  On a fast processor with a highly
contentious application where response time is critical, this is a good
choice.  An option argument to the <a href="../../api_c/env_set_lk_detect.html">DB_ENV-&gt;set_lk_detect</a> method
indicates which lock requests should be rejected.</p>
<p>The application can limit how long it blocks on a contested resource.
The <a href="../../api_c/env_set_timeout.html">DB_ENV-&gt;set_timeout</a> method specifies the length of the timeout.
This value is checked whenever deadlock detection is performed,
so the accuracy of the timeout depends upon the frequency of
deadlock detection.</p>
<p>In general, when applications are not specifying lock and transaction
timeout values, the <a href="../../api_c/env_set_lk_detect.html#DB_LOCK_DEFAULT">DB_LOCK_DEFAULT</a> option is probably the
correct first choice, and other options should only be selected based
on evidence that they improve transaction throughput.  If an application
has long-running transactions, <a href="../../api_c/env_set_lk_detect.html#DB_LOCK_YOUNGEST">DB_LOCK_YOUNGEST</a> will guarantee
that transactions eventually complete, but it may do so at the expense
of a large number of lock request rejections (and therefore, transaction
aborts).</p>
<p>The alternative to using the <a href="../../api_c/env_set_lk_detect.html">DB_ENV-&gt;set_lk_detect</a> method is to
explicitly perform deadlock detection using the Berkeley DB
<a href="../../api_c/lock_detect.html">DB_ENV-&gt;lock_detect</a> method.</p>
<p>The <a href="../../api_c/env_set_lk_conflicts.html">DB_ENV-&gt;set_lk_conflicts</a> method allows you to specify your own
locking conflicts matrix.  This is an advanced configuration option,
and is almost never necessary.</p>
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